Action potentials from single neurons in the limbic system of unrestrained rats will be recorded extracellularly, and the relation of activity of neurons to the behavior of the rat will be determined. A wide range of behaviors, is observed, including slow wave sleep, paradoxical sleep, quiet arousal, eating, drinking, grooming, defecation, escape and active avoidance of tail pinching, passive avoidance; visual tactile, auditory, and olfactory inputs: interruption of ongoing activity and response to novel objects. The aim is to identify behaviorally defined types of neurons in various parts of the hippocampal formation. Electrophysiological experiments on behaviorally identified neurons have been done.